Today I tried my G7RGQ antenna together with a NooElec NESDR Smart stick connected to the ADSB Raspberry Pi. I put the antenna and the stick on the roof and had it running for a while. To my surprise the performance was not as expected. I needed the same a gain setting to archive results comparable to my QFH antenna with 6m coax to the receiver. Again, I removed 6m of coax, around 6dB attenuation, but results were ain´t better. Took everything down again and disassembled the setup for testing.
For a test setup I used my Rohde&Schwarz FSH spectrum analyzer to generate a signal at 1090MHz and SDR# to tune and monitor the reception. For comparison I tested three SDR sticks, 1) NooElec NESDR Smart 2) FlightAware SDR Pro stick and 3) general E4000 SDR stick.
The FSH was set to:
- zero span (single frequency CW output)
- tracking generator enabled
- tracking generator attenuation 20dB
An external attenuator with 30dB was connected between the tracking generator output and the SDR sticks. The input to the stick was around -50dBm then. I have not measured absolute levels but compared the relative levels at 1090MHz of the sticks indicated in SDR#. No gain was used.
While the input conditions for all sticks were the same, the outcome is a bit different, at least for the NESDR stick. The E4000 and FlightAware stick are sampling under the given input conditions close to the full scale maximum. The NESMART in turn shows a level of -12dB less than the other two sticks.
This -12dB less seems to be the reason for the bad performance I noticed in dump1090.
The NESDR Smart is a nice piece of hardware compared to other sticks. I had chosen it in the latest setup over the FlightAware SDR stick because of its slim design that nicely fitted inside the antenna pole. But the performance, at least for ADSB at 1090MHz is a NOGO for me. I have not compared other frequencies so can´t say whether it performs better at lower frequencies.
As a solution I modfied the antenna again with new pole that fits the FlightAware Pro stick including the ADSB bandpass filter. I hope it performs like on the bamboos pole a week ago.
By the way, that E4000 stick is not usable for ADSB at all, it has no TCXO and a frequency drift like hell.